Distillation of sulfuric acid treated hydrocarbon oils



Patented July 20, 1948 Harry L. Allen and Herbert G. Philadelphia, Pa., asslgnors to Allied w at r, Chemical 3; Dye moratfim, New zlzoilh illseem? retire at How Flori;

Arrl cafl nfiertcmb 1348,

Ser al No. (CLW) 1 invention relates to the refining of aromatic distillates, .particul-arlyithose distiilates :o'htained from coal-tar, wateregas tar and-oils rob.- ttained from carburetted water-gas operations. it is particularly applicable in the refining f dis tillates derived from these sources which have been treated with sulfuric acid and aneutralizagent.

In the refinin of aromatic hydrocarbon oils to obtain sci-called water-white distillates which are used as solvents, for example in the paint and varnish industry, or as raw materials tor chemical syntheses, or as fuels for internal combustion engines, it is customary to treat the oils or fractions thereof with concentrated sulfuric acid, a neutralizing agent such as -aqueous-caustlc soda solution and then fractionally distil the neutralized oils to recover the desired fractions of refined water-whiteofls. In many cases, the oils-are washed -water prior tothe fractional distillation step. During the distillation there is frequently encountered a copious evolution of sulfur di xid parti ularly in the case of oils d rived from water-gas tar anddrippilxtoils co llecting in manufactured gas distribution mains and holders or which arescrubbed from manufactured gas during its recovery). The :sulfur dioxide thus evolved causessevere corrosion of the still, fractionating column, -.condenser and other parts of the distillation equipment. When steam is used in the distillation the corrosion is particularly severe owing to the formation of the highly-corrosive sulfurous acid. Furthermore, the sulfur dioxide passes into the distillate products imparting to them an objectionable acidity which must be neutralized or removed before a saleable product can be obtained.

This evolution of sulfur dioxide is due apparently to the breakdown under distillation conditions of various thermally-unstable materials such as organic sulfates and related compounds introduced during the treatment with sulfuric acid and not removed by the subsequent treatment with aqueous neutralizing agent. Various attempts have been made to combat the evolution of sulfur dioxide and the resultant deleterious effects but these attempts have generally been only partially successful or require a large quantity of reagent.

It is an object of this invention to provide an improved process for refining aromatic hydrocarbon oils.

It is a further object of this invention to provide an improved method of distilling aromatic hydrocarbon oils whereby 'a'the evolution of sulfur dioxide-is suppressed.

Other objects and ad vantagesmiiiappear'zheree inafter.

In aceordancewith :oursinvention, an aromatic hydrocarbon oil which hafibeenre'fined icy treat. ment withconcentrated sulfuric acid and a new traliz'ing agent, fer exam-pie aqueous caustic soda solution, is distilled in the presence of urea "or thiourea. The expression arematic hydrocarbon oil isused herein-to refer tothose oils and fractions "thereof predominately aromatic incharacfter recoveredirom coaltar and water-gas tar rcbtained in "the coking of coal or in the manuiaQture of carburetted -water-gas and including oils such as drip oil collecting in manufactured gas distributionand'storage systems or scrubbed from 'imanufactured gas during its recovery.

'We have found that distilling -acid treated and neutralized aromatic hydrocarbon oils in the rese l e of urea "ortf-himirea, evolution of sulfur 'dio glde is substantialiy eliminated. rts'ziniiicated above, our improved process is particularly applijcable to the distillation of oils derived from drip oil and from 'carburctted water-gas opera tioussince such oi s have a nde cy to m"Sl-.'tb'- tant 'sl 't v e com unfl 'w Wen si bseauen distillation a e re ponsihieiror the evdlutionoi sulfur dioxide. The processiis especially applicable to treatmentoi "oil fractiens boiling within the range of from "C.'to 250 C.

We have found that urea or thiourea even when used in small quantities is surprisingly effective in preventing the evolution of sulfur dioxide and the attendant deleterious effects upon equipment and product during the distillation of acid-refined aromatic hydrocarbon oils. The invention may be carried into efiect for example, by subjecting an oil, such as drip oil benzenetoluene fraction, boiling within the range of from about 70 C. to about C., to the action of concentrated sulfuric acid, separating the acid sludge from the oil, washing the oil with an aqueous solution of a neutralizing agent, such as aqueous caustic soda, washing the neutralized oil with water and then fractionally distilling the oil in the presence of urea or thiourea to obtain a refined water-white oil requiring no further treatment. The distillation may be carried out at atmospheric pressure or at subatmospheric pressure, with or without the use of live steam and either batchwise or continuously.

The amount of urea or thiourea necessary to secure optimum inhibition of sulfur dioxide evolution depends on various factors including the scale distillations of small portions of the batch with different amounts of the reagents and test:.

ing the vapors for the presence of sulfur dioxide. The agent may be added directly'as a solid to the oil to be distilled or it may be. added asa solution in a solvent.

invention:

1. An oil fraction of drip oil within the range from 70 to 140 H from which benzene and toluene may be recovered origin,. boiling C., a fraction,

"lates without further treatment.

Since certain changes may be made in the above described process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpretedas illustrative and not in a limiting sense i v a Wejclaim': The following examples are illustrative of the- 1. In the'refining of an aromatic hydrocarbon oil by treatment with sulfuric acid and subsequent distillation, the improvement which comby fractional distillation, previously treated with sulfuric acid and caustic soda solution, was distilled in the presence of 0.1% of urea (based on the weight of the oil). No sulfur dioxide was evolved throughout the entire course of the distillation.

- For purposes of comparison another portion; of

the same oil fraction was distilled in the absence of any urea. Byt'he time the temperature-ofthe Vapors being distilled had reached 133 C., evolution of substantialquantities of sulfur dioxide had begun. Sustainedevolution of sulfur dioxide as in the case of continuous operation would have led tocorrosion of the distillation equipment.

2. An. oil fraction of drip oil origin having a boiling range of 120 to 170? 0., previously treated with sulfuric acid and caustic soda solution, to which 0.1% of urea (based on theweight of the oil) had been added was distilled and tests for sulfur dioxide made during-the course of the dis tillation- Seventy-three per cent of the oil .fraction haddistilled, i, e., vapors had reached 165 C. before sulfur dioxide was detected. 1 For purposes of comparison, a portion of the same oil fraction to which no urea had been added was distilled. Sulfur dioxide became noticeable when only six per cent of the oil fraction had distilled. a 3. Another portion of the same oil fraction employed in Example 2was distilled after the'addition,,of'0.1% of thiourea. 'Forty-eight percent of the oil fraction had, distilled before evolution of sulfur dioxide began. Y

1 prises-g eliminating excess acid from the acidtreated oil and thereafter distilling the oil in the presence of a compound selected from the group consisting of urea and thiourea.

2.- In the refining of an aromatic hydrocarbon oil by treatment with sulfuric acid and subsequent distillation, the improvement which comprises washing the acid-treated oil with caustic soda solution to neutralize excess'acid and distilling the washed oil in the presence of between 0.1% and 1% by weight of at least onecompound se lected from the group consisting of urea and thiourea.

-3. The process of the preceding claim wherein the oil is separated from acid prior to washing and from caustic soda solution prior to distilling and to the separated oil between 0.1% and 1% by weight of urea is added prior to the distillation.

4. The process of the preceding claim wherein the oilis adrlp oil distillate fraction of boiling range between C. and 250 C.

' HARRY L. ALLEN.

HERBERT G. KLEINGUENTI-IER.

v REFERENCES CITED The following references are of record in the file'of this patent:

I UNITED STATES PATENTS Number 

